In methods a and b above, the pump will remain primed, provided foot valve is tight. Any failure,
however, of foot valve when pump is standing idle, will permit the pump to lose its prime. During
long idle periods, the pump can also lose its prime through leakage from stuffing boxes.
c)
Bypassing Around Discharge Check Valve: This method can be used only when there is liquid
under some pressure in the discharge line. The original prime must be effected from some out-
side source. After subsequent idle periods, open air vent valves and open valve in bypass line
around discharge check and gate valves until liquid flows from air vent openings. Close air vent
valves and bypass valve, start pump and open discharge gate valve.
1. Foot valve
4. Discharge gate valve
2. Air vent valves
5. Shut off valve
3. Discharge check valve
6. By-pass line
Figure 44: Bypassing
The valve in bypass can be left open, in which event, during idle periods, loss through foot valve is
constantly replenished from discharge line. This system is used for automatic operation where idle
periods are of short duration and there is no danger of exhausting all liquid from discharge line, due
to a leaky foot valve. The foot valve must be capable of withstanding static head pressure of the
system.
3.
Priming by Ejection
a) On suction lift installation, an ejector, operated by steam, compressed air, or water under pres-
sure, and connected to tapped opening in top of casing can be used to remove air from casing
and suction line, thus priming the pump. See image below.
5.14 Priming
3175 Installation, Operation and Maintenance Instructions
41
